1. Technical Field
Exemplary aspects of this disclosure generally relate to an image forming apparatus, such as a copier, a printer, a facsimile machine, a plotter, or a multifunction machine capable of performing at least two of these functions.
2. Description of the Related Art
In electrophotographic image forming apparatuses, imaging conditions (e.g., a charging bias, a development bias, operation of an exposure device) are adjusted to maintain a certain image density. More specifically, a test toner pattern is formed on a transfer belt that bears the toner and a reflection light detector (optical detector) detects an amount of toner adhering (hereinafter toner adhesion quantity) to the test-toner pattern. Based on the detection result obtained by the optical detector, the image forming apparatus adjusts one or more of the imaging conditions in a toner-image formation unit.
After the test toner pattern is formed on the surface of the transfer belt, the reflection light detector detects not only the amount of light reflected from the test pattern but also the amount of light reflected from a clear area of the transfer belt on which the test-toner pattern is not formed. Then, the image forming apparatus compares the two readings and estimates the toner adhesion quantity of the test toner therefrom.
However, since the amount of light reflected by the belt fluctuates depending on the location, the toner adhesion quantity cannot be estimated accurately if the detected positions between the toner-adhered test pattern and the surface of the transfer belt differ.
Accordingly, in the known image forming apparatus, the amount of light reflected from the surface of the transfer belt has been detected in advance at least one revolution before, and then the test-toner pattern is formed and the amount of light reflected from the test-toner pattern is detected. Thus, the detection position where the toner-pattern output is detected and the detection position where the surface output is detected are located at the same position, which allows the toner adhesion quantity to be properly detected.
However, in the above-described apparatus, whenever the toner adhesion quantity is estimated, it is necessary to make the transfer belt rotate one revolution or more before the test-toner pattern is formed, thereby lengthening downtime. The downtime can be minimized by reducing the frequency with which the toner adhesion quantity is estimated, but doing so degrades the toner adhesion quantity estimates and imaging condition control precision deteriorates, possibly resulting in unstable image density.
In order to prevent the downtime from lengthening due to the toner adhesion quantity estimation process, it is possible to obtain the output of the surface in advance at a time when lengthening the downtime is acceptable (e.g., when the transfer belt is replaced) and using only the toner output readings to estimate the toner adhesion quantity. In this method, the toner adhesion quantity is estimated using the toner-pattern output detected and the surface output detected in the portion identical to a portion in which the test-toner pattern will be formed and stored in memory. Therefore, it is not necessary to make the transfer belt rotate one or more revolutions before the toner pattern is formed, which prevents the downtime from lengthening.
However, such previously stored information does not adequately account for the effects of changes in the amount of light reflected from the surface caused by scratches and grime generated when the transfer belt comes into contact with other parts of the apparatus and which are not reflected in the estimation operation. As a result, the toner adhesion quantity might not be estimated accurately.
Moreover, although a configuration in which the image bearing member on which the toner image is formed is the transfer belt is described above, a similar problem may occur with a drum-shaped intermediate transfer member or a belt-shaped or drum-shaped photoreceptor. Further, the toner information is not limited to that which is detected by the relation between the amounts of light reflected from the toner-adhered test pattern and that from the surface of the image bearing member directly.